Just How Common Is Lumbar Spinal Stenosis in the U.S.?

Despite the fact that spinal stenosis (narrowing of the spinal canal) affects a large number of people over age 60, there are still many things about this condition we don't know. For example, when does narrowing of the spinal canal actually become stenosis? Is it when the spinal canal opening is less than 15 mm? 12 mm? 10 mm? Are there certain groups of people more likely to develop stenosis than others? How many people really have this condition anyway? And of those folks who do have stenosis, how many have low back pain caused by the stenosis?

The authors of this study used data from the Framingham study to help answer some of these questions. The Framingham study started out in 1948 as a heart study looking at cardiovascular disease in a group of people living in Framingham, Massachusetts. Over time, as the second (and now third) generation family members have been included in the study, data collected has been used to evaluate other things besides heart disease.

In this study, they used CT scans of participants taken for other reasons to look at the size of the spinal canal indicating spinal stenosis. For their own purposes, the authors defined stenosis as relative when the opening was narrowed down to 12 mm. Absolute spinal stenosis was defined as 10 mm or less. The measurement refers to the anteroposterior (front to back) diameter of the spinal canal. These values were chosen because they have been used in many other studies and that makes it possible to compare results from study to study.

Two types of stenosis are recognized: congenital (something you are born with) and acquired. Acquired develops and progresses over time, usually being age-related or degenerative. Adults over age 60 seem to be most susceptible to acquired lumbar spinal stenosis. Patients in the sample selected for this study ranged from 32 years of age up to 79 years old.

As part of the Framingham study, CT scans were taken of the abdomen and chest looking for hardening of the coronary and aortic blood vessels. The participants also completed a special questionnaire called the Nordic Low Back Questionnaire that identified who had low back pain. Of the 3,590 people who had the CT scans done, 191 were included in this study. Pain was reported most often in the buttocks or thighs, followed by pain in the lower leg, numbness in the leg or foot, and less often, weakness in the leg or foot.

Acquired lumbar spinal stenosis is much more common than congenital. Relative stenosis is much more common than absolute stenosis in all age groups. Not everyone had pain; some people were completely free of symptoms. Clearly, the number of people with lumbar spinal stenosis rises with age. But in order to isolate the specific decade when acquired stenosis becomes more of a problem, the participants were grouped four ways: 1) younger than 40, 2) 40 to 49 years old, 3) 50 to 59, and 4) 60 and older.

What they found was that the prevalence of absolute stenosis (narrowing was 10 mm or less) was most often observed in adults ages 40 to 60 and above. And this was also the group most likely to develop painful low back symptoms. Men and women were affected equally, so there was no difference between the genders. The overall prevalence (how many people have this problem on any given day) for all age groups was 4.7 per cent for relative lumbar spinal stenosis and 2.6 per cent for absolute lumbar spinal stenosis. Just looking at the 60+ age group, these percentages increased dramatically to 47.2 per cent for relative stenosis and 19.4 per cent for absolute stenosis.

The authors concluded there were three major findings in this study: 1) This was the first study calculating the prevalence of lumbar spinal stenosis for a cross-section (wide range) of people, 2) Acquired lumbar spinal stenosis increases with age, and 3) Just because you are over 60 and have visible stenosis on CT scans doesn't mean your back pain (or other stenosis-like symptoms) are coming from the stenosis. On the other hand, if you are over 60 and you do have stenosis, your chances of developing low back pain increase by a factor of three. In other words, you would be three times more likely to experience back pain compared to someone your same age who doesn't have stenosis.

Leonid Kalichman, PhD, PT, et al. Spinal Stenosis Prevalence and Association with Symptoms: the Framingham Study. In The Spine Journal. July 2009. Vol. 9. No. 7. Pp. 545-550.

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